Wireless systems have conventionally been designed to efficiently handle the transfer of data between a single network node, e.g., base station, and a single terminal, e.g., user equipment (UE), for standard communication frequencies, e.g., 1-2 GHz. The need for higher capacity, however, is resulting in a shift to higher carrier frequencies and/or transmissions by multiple network nodes, which is generally referred to as multi-point transmission.
The shift to higher carrier frequencies typically reduces the useful power experienced by the receiver. In particular, higher radio frequencies cause the radio propagation to transform from a diffuse scattering to a more beamlike propagation. The resulting sharp diffraction effects and increased radio shadowing (e.g., behind obstacles) makes it more difficult to achieve uniform coverage from a single base station. Multi-point transmissions, where data is transmitted from multiple non-co-located transmission points to a receiver, e.g., from multiple base stations to a single mobile station, may be used to provide more uniform coverage. Such multi-point transmissions may be used for various wireless systems, e.g., 4G and 5G systems.
Conventional multi-point systems typically involve a small number of transmission points, e.g., two transmission points. However, the higher frequencies and higher capacity requirements of newer systems are expected to require a large number of transmission points. Conventional systems and solutions, however, are unable to sufficiently control the synchronization errors, particularly those too large to be handled by existing protocols, and/or the large numbers of transmission points expected with such large multi-point systems. Thus, there remains a need for new ways to control multi-point systems.